Field of the Invention
This invention relates to real-time three-dimensional (3-D) object tracking and alerting using networked overlapping two-dimensional (2-D) sensors to observe objects and image processing (IP) tools to detect and track the moving objects.
Description of Related Art
Physical perimeter security is an ever-growing and challenging problem. Human observation of sensor displays can be quickly overtaxing. Most physical perimeter security systems use closed circuit television, monitored continuously by security personnel.
There is a need for enhanced physical perimeter security, particularly the automated tracking of threatening objects, and especially the simultaneous tracking of multiple ground, surface (water), and airborne targets with high precision and in three dimensions. The migration from analog to digital cameras, the networking of these digital cameras, and the use of video analytics to assist the monitoring security personnel makes meeting this need more possible. This technology has many uses, including physical perimeter security, military asset protection, border control, and traffic applications.
Prior attempts using passive cameras merely involve two-dimensional (2-D) image processing. These prior attempts do not use triangulation methods with overlapping coverage from multiple cameras. Instead, they use complementary camera coverage, which fails to resolve target range adequately. As a result, the target tracks, if even possible, tend to be highly erroneous. An attempt to solve this problem by using an accurate terrain map of the camera field-of-view and using the camera-to-target vector to find its “piercing point” on the terrain could be adequate in limited cases (e.g., high target “grazing” angles). Even then, these systems cannot provide airborne target tracks without triangulation because the “terrain piercing” approach is no longer applicable.
Due to these limitations, alert generation using current methods works only on very simple target behaviors, such as crossing a line on a 2-D representation of the area under surveillance. Such alerts result in uncertainty that hinders effective countermeasures and interdiction. In fact, since the 2-D “line” is actually a 3-D “plane,” nearby objects of no significance (such as birds) may accidentally set off the alert, thus triggering a false alarm. Another way to create 3-D tracks is with active radar capable of providing range, range rate, azimuth, and elevation observations, but no passive electro-optical/infrared system currently has this capability.
Competing systems are limited to analog or IP-based sensors and detection software. Most cannot track ground (terrestrial) or surface (on water) targets and even those that can lack precision and require extensive knowledge of the terrain involved. None can track airborne targets. Most use alert rules based on image analysis, e.g., (1) trip wire (setting off an alert based on an image crossing a predefined line), (2) object left behind (one object enters, then departs leaving a stationary object behind), (3) object removed (one object enters, then departs after taking a stationary object), (4) counting (e.g., people, cars). These lack airborne tracking ability and at best have only limited ground tracking ability.
Traditional fixed camera systems use a few wide field-of-view (FOV) cameras with minimum coverage overlap. There is limited tracking capability, and only for ground targets, but the cameras are not very expensive. Alternatively, a fewer number of (usually) higher-priced pan-tilt-zoom (PTZ) cameras can provide some visual tracking capability (through panning) and target identification (through zoom), but require subjective selection of targets with potential coverage loss as a result.
Thus, there exists a need for a system and method for real-time three-dimensional detection, tracking, and alerting of moving objects using conventional sensors, especially passive ones.